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Tuesday, June 24, 2014

Chessmen Complete

I finished the medieval chessmen project. All the pieces are resin-cast and weighted with green felt bottoms and were painted with acrylics. I ended up doing several more 3d prints before moving forward with casting as I worked out the kinks in the design.

While sanding away the artifacts left over from the printing supports, I realized I was sanding away the finer details on the king and queen. To fix this, I split the king in two in Zbrush and added registration markers so the pieces fit together when I reprinted them. This way, all the support artifacts were on the flat pieces of the model that wouldn't be seen. I repeated the process for the queen.

Dividing walls in Wed Clay. All the molds were two piece molds except the King and Queen which were just block molds, that way I didn't have to worry about the crowns being broken in the dividing the wall.

Molds after pouring. Just foam core that was hot-glued to a piece of wood around the clay dividing walls. I poured Mold Star 15 Platinum Silicone about 1/4'' over the highest point of the model. Mold Star 15 takes 4 hours to cure. This photo was taken after the first side was cured. I then flipped the foam core over to reveal the clay on the bottom. Remove the clay but leave the model, the foam core, and the first half of the mold in place. I greased the silicone with vaseline so the second half of the mold wouldn't stick. If you skip this step, you will end up with a block mold as the silicone doesn't stick to anything but itself.

Don't forget to add a sprue before pouring the second half of your mold so you have somewhere to pour resin into the mold.

Finished molds and started my test casts.

Troubleshooting casts. In the end, some of the smaller areas like the crowns and the ears of the knights wouldn't cast well so I used resin putty to fix (or in the case of the crowns, resculpt) the areas that weren't coming out right. Most problem areas were usually the result of air getting trapped inside the mold. With the test casts, I could find areas that needed to be vented (the jaw and the base of the knight as seen above) so I used a some small gauge copper tubing to punch holes in the right areas to allow air to escape. You can find copper tubing at most hobby stores, I believe it was in the model car section.

Originally, I thought I would just pour up all the molds at once. I thought wrong. I used Smooth-Cast 320 which has a demold time of 10 minutes and a pot life of 3 minutes (less on a warm day). That just wasn't enough time (at least for me) to get all the molds poured and gently rotate each one to make sure the air bubbles rose to the surface. I ended up doing 1-2 at a time and then I would prep the other molds while I waited for the first ones to cure.

I left holes in the bottoms of the pieces to both save resin for the 3d printer as well as leave a space for the pieces to be weighted and then filled in with more resin.